For today's militant atheists it must be inexplicable and frustrating that religion continues to engage men and women of the highest intelligence. If the grounds for faith are so easy to demolish, how is it that all the most brilliant minds have not recognised this long ago? That they haven't is attested by the continuing recruitment of fine intellects into the ordained ministry of all the mainstream denominations of the church and by the flourishing of religion in our ancient universities.

And yet there is absolutely no doubt that adherence to all the main Christian churches in western Europe has massively declined in recent decades, and religious communities seem to be waging a losing battle for hearts and minds - especially minds. At the same time there remain buoyancy and real numerical growth in the more simplistic, evangelical reaches of the church. How do we account for these two paradoxical factors - what we might call the eggheads and the sheep - spoiling the beautiful Dawkins vision of a religion-free future?

Baron Friedrich von Hügel, the early 20th-century Roman Catholic thinker, wrote of three elements of religion. In the institutional element, a child, for example, soaks up with delight and few questions all the customs and creeds of the religious institution. The second intellectual element most typically begins in adolescence, when individuals begin to pose questions to the inherited faith and attempt to make sense of it for themselves. If they fail in the quest of this second element, they may well abandon their childhood faith and its related institution. But if they succeed, they move on into the third or mystical element of religion, when - without in any way leaving behind the first and second elements - they are able to live with questions that no one can answer, exploring the connections of thought and feeling which help make belief not a groundless or fruitless activity, and living in an attitude of wonder and ultimate trust in the universe.

Now it seems to me that highly gifted people are often able to move naturally and with deep fascination into Von Hügel's third element of religion. They do not in the process leave behind the institutional and intellectual aspects of faith, and this gives them a rich multi-dimensional grasp on reality and meaning - something very different from certain and final knowledge. Many in our time have continued to be able to leap across to maturity of faith. At the other end of the spectrum, however, the simple (and the faux-simple), like the poor, we always have with us in the churches.

But what I think happened, especially from the 1960s onwards in Britain, was that vast numbers of pew-sitters were tempted by forces mostly inside the church, but also by the new social and economic freedoms, to start asking questions and to move on from their simple institutional religion to the questioning of the second element; and that most of them had been talked out of their church adherence before they could get anywhere near a fuller, mystical phase of belief.

And that is why - in an oversimplification which nevertheless contains some truth - today's church is full of intellectuals and simpletons. The only nuances I would add to this stark claim are: that many reasonably intelligent people, including ministers, choose to compartmentalise religion as an area of childlike, institutional belief and so stay uncomplainingly alongside the genuinely simple; while, on the other hand, people of only modest intellectual attainments are more capable than many clergy imagine of moving through the tough questions to a deeper awe and trust.

There are, I think, a lot of arrested religious adolescents out there. The tantalising truth for the churches is that there is somewhere for those people - spiritually and theologically - to go. But can they find the way to it in their local pews?